Abstract Adolescents with intellectual and developmental disabilities (IDD) are less physically active and have lower cardiovascular fitness compared with their typically developing peers. Adolescents with IDD also face additional barriers to participation in moderate-to-vigorous physical activity (MVPA) including dependence on parents for transportation to exercise facilities, lack of appropriate exercise facilities, lack of PA professionals with expertise regarding the specific needs of adolescents with IDD, and lack peer support. Previous interventions to increase MVPA in adolescents with IDD have met with limited success, at least in part due to requiring parents to transport their adolescent to an exercise facility, which represents significant barrier to families already dealing with the burden of providing routine care for a special needs adolescent. We recently developed a remote system to deliver MVPA, led by a trained health coach, to groups of adolescents with IDD in their homes via video conferencing on a tablet computer. This approach eliminates the need for transportation, provides social interaction and support from both the health coach and other participants, and is feasible with minimal parent involvement. We propose an 18 mo. trial (6 mos. active, 6 mos. maintenance, 6 mos. no-contact follow-up) to compare changes in objectively assessed MVPA in 114 adolescents with IDD randomized to a single level intervention delivered only to the adolescent (AO) or a multi-level intervention delivered to both the adolescent and a parent (A+P). Adolescents in both intervention arms will be asked to attend home-based, group MVPA sessions conducted by a trained health coach using video conferencing software and to complete a weekly activity homework assignment. Parents of adolescents in the A+P group will be asked to participate in the group video MVPA sessions and homework activity, attend educational/support sessions with their adolescents regarding the role of MVPA in health and function and strategies for increasing MVPA in both their adolescent and themselves, and will be provided access to a Facebook page to interact with parents of other adolescents in the A+P arm. Our primary aim is to compare mean increases in MVPA (min./d) between the AO and A+P groups from 0 to 6 mos. Secondarily we will compare changes in MVPA, sedentary time, cardiovascular fitness, muscular strength, motor ability quality of life and the percentage of adolescents achieving the US recommendation of 60 min. MVPA/d across 18 mos. We will also explore the influence of process variables/participant characteristics including attendance at group video (AO-adolescent; A+P-adolescent/parent) and education/support sessions (A+P only), self-monitoring of MVPA (AO-adolescent; A+P-adolescent/parent), parental use of Facebook page (A+P only), peer interactions/support during group PA sessions, adolescent self-efficacy, social support and barriers for PA, parental MVPA, beliefs and attitudes toward PA and parental time constraints, age sex and IDD diagnosis.